Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, ect.). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), evolution data optimized (EV-DO), etc.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Further, communications between mobile devices and base stations may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or base stations with other base stations) in peer-to-peer wireless network configurations.
To supplement conventional base stations, additional low power base stations can be deployed to provide more robust wireless coverage to mobile devices. For example, low power base stations (e.g., which can be commonly referred to as Home NodeBs or Home eNBs, collectively referred to as H(e)NBs, femto nodes, femtocell nodes, pico nodes, micro nodes, etc.) can be deployed for incremental capacity growth, richer user experience, in-building or other specific geographic coverage, and/or the like. In some configurations, such low power base stations are connected to the Internet via broadband connection (e.g., digital subscriber line (DSL) router, cable or other modem, etc.), which can provide the backhaul link to the mobile operator's network. In this regard, low power base stations are often deployed in homes, offices, etc. without consideration of a current network environment.
OFDM have the ability to mitigate delay spread. This delay spread is the difference between the earliest and latest arriving signal instances (multipath) at a receiver for a signal transmitted via the wireless channel by a transmitter. These signal instances may have traveled via direct paths and indirect reflected paths formed by obstructions in the environment. The received signal at the receiver is a superposition of all of the arriving signal instances.
Delay spread causes intersymbol interference (ISI), which is a phenomenon whereby each symbol in the received signal acts as distortion to one or more subsequent symbols in the received signal. The ISI distortion degrades performance by impacting the receiver's ability to correctly detect the received symbols. Delay spread can be conveniently combated with OFDM by repeating a portion of each transformed symbol to form an OFDM symbol. The repeated portion is called a cyclic prefix or a guard interval. The cyclic prefix length is equal to the number of samples that is repeated for each transformed symbol.
The cyclic prefix length determines the amount of delay spread that can be combated with OFDM. A longer cyclic prefix length can combat more delay spread. An overprovisioned cyclic prefix length represents extra overhead for each OFDM symbol.
Standard cyclic prefix lengths are often overprovisioned in benign channel conditions with a smaller delay spread. This is especially common with the advent of low power base stations. Therefore, there is a need in the art for techniques to better utilize cyclic prefix resources in OFDM systems under benign channel conditions.